Investigation On Recognizing Event Position In Fiber-optic Distributed Disturbance Sensor Based On M-Z Interferometer

The distributed optical disturbance sensor based on fiber-optic interferometer with a high sensitivity and the advantages of the continuous distributed location detection, has a wide range of applications in fields such as petrochemical industry, biological, power system and so on. Many solutions for distributed sensors are proposed at home and abroad, and of which, M-Z(mach-zehnder) interferometer structure is a popular scheme. M-Z interferometer disturbance sensor system can perform the continuous distributed detection at any point along the sensing fiber, which determins the position with the sensing time delay estimation. Therefore, the time delay estimation method for the M-Z interferometer fiber distributed sensing system have important effects on positioning resolution and positioning error. This article focuses on the event position method in optic-fiber disturbance sensor based on Mach-Zehnder interfermoter, the researching results of this thesis can be described as follow:Firstly, the developing situations for optic-fiber disturbance sensor based on Mach-Zehnder have been studied, mainly focusing on the key technologies, especially the position method development and existing problems. This paper investigated the basic structure, its sensing mechanism and have got the relationship between the light from the laser source with the disturbance. The function between the position and the delay have been also deduced.Secondly, this thesis introduce some position method principles and applications in Mach-Zehnder interferometer optical sensing system, especially cross-correlation function and cepstrum time delay estimation.To reduce the position errors with cross-location method, based on the analysis of the location principle of the fiber-optic distributed disturbance sensing system based on Mach-Zehnder interferometer, this paper proposes a location method with Lissajous figure for determining the position at which disturbance signal occurs. By analyzing and processing the Lissajous figure synthetized by signals of actual signals, the fitting ellipse can be obtained by fitting the acquisition data. The relations between elliptical parameters and the delay are investigated in detail. Experimental results illustrate that semi-major axis and semi-minor aixs of the ellipse are in a linear relation to delay time and the semi-minor axis is more sensitive to delay time. By evaluating the semi-minor axis, disturbance position can be determined.The proposed location method has a lower positioning error than cross-correlation method and can provide a beneficial reference on location methods for fiber distributed disturbance sensing system.